Identification: A small (up to 18mm in
height and 14mm wide), ovoviviparous, dioecious, herbivorous snail
occurring either in off-white, greenish, reddish or brown colors.The aperture of the shell is large, rounded
and has a slightly everted lip.The throat of
the shell is darker.The shell is plump with
4-5 whorls and deep sutures.

Original Distribution:Littorina saxatilis has a wide
dispersal in the Atlantic
Ocean occurring on both
the east side and the west side.It occurs in
intertidal zones in salt marshes and subtidal hard substrates.It is also found in crevices of bedrock, empty barnacle
shells and under rocks. In salt marshes, it can be found on the base of Spartina species.It may also be
found on firm mudbanks as well as submerged in brackish water attached to
Zostera, Fucus, Ruppia and Potamogeton species.There are maximum reported densities of well over 100,000
snails m-2.

Current Distribution: Littorina saxatilis is currently
invasive in the San FranciscoBay area.Littorina saxatilis also has been found at three isolated sites
in the South Atlantic (Namibia and South Africa), likely representing introduced populations.

Site and Date of Introduction:San FranciscoBay, 1992

Mode(s) of Introduction: There is no certainty of mode of introduction.However, it is the general concensus that the invasion
was likely due to the association with bait or live seafood transport.They have been associated with an Atlantic alga (Ascophyllum
nodosum), which is often used as packing material for shipments
of live animals.

Reason(s) Why it has Become Established:Littorina saxatilis is
successful in becoming established in a previously foreign area in that it
has a capacity to feed on newly settled barnacles and can compete successfully
with other like organisms for food supplies.The
study described below intends to pursue further research on successful invasion
of this species.

Ecological
Role:This snail is primarily
herbivorous and is known to affect algal bloom dynamics and can prey upon
newly-settled barnacles

Benefit(s): Unable to find any evidence on this front.

Threat(s):Observations of the behavior of Littorina saxatilis in the Atlantic have
spawned predictions that it may have significant long-term impacts on Pacific
nearshore ecosystems all up and down the coast as it continues to spread
and increase in population density. Studies performed on other similar,
invasive, herbivorous snails have revealed that they have had serious ecological
impacts on receiving ecosystems.

Control Level Diagnosis: Some experts believe that the rough periwinkle
should be easily eradicated.For one thing, it
does not possess a larval stage of development which would increase its chances
of spreading via a “free floating state” to other areas. So far, its invasive
range is believed to be restricted to areas within the San Francisco region that are easily accessible so that collections
methods could be executed with relative ease.If
eradication begins, it should begin while the species is still confined to
the San Francisco area, as its potential growth could reach from
Baja California to Alaska. Previous eradication work has proven that early
action may be imperative.

Control Method: No method is
yet forthcoming for the removal of this specific species.In general, biocides, manual removal of marine invaders, and
the introduction of biocontrol agents have
been considered in the removal of invaders of marine systems. However, little
has been done in the way of eradication and, in addition, pursuing research
in this area in general.There is concern that
any research to be conducted should include the study of ways to avoid reintroduction
of the species.A study sponsored by NOAA and
the SmithsonianEnvironmentalResearchCenter is underway to determine if Littorina
saxatilis can be eradicated from the San FranciscoBay area.The SmithsonianEnvironmentalResearchCenter is also attempting to determine population and
expanse of the rough periwinkle the Bay area. In
addition, they are measuring the genetic and demographic changes associated
with the recent invasion of the rough periwinkle by comparing newly colonized
populations in San FranciscoBay to populations in its native
range and source locality.